A field effect transistor (FET), such as an NFET or a PFET, typically includes shallow, lightly doped extension regions situated in a silicon substrate adjacent to a channel region, which is situated under a stacked gate structure. The FET further includes deep, heavily doped source and drain regions, which are situated under the extension regions and also situated a certain distance away from the channel region in the silicon substrate. However, the distance between the source and drain regions and the channel region must be sufficient to prevent the heavily doped source and drain regions from over-running the lightly doped extension regions and causing undesirable short channel effects in the FET.
During FET fabrication, a desired distance between the channel region and the source and drain regions can be maintained by forming disposable spacers adjacent to the sidewalls of a stacked gate structure prior to formation of the source and drain regions. During a conventional disposable spacer process, a oxide liner is generally formed over the stacked gate structure and on the silicon substrate adjacent to the stacked gate structure. Conventional disposable spacers, which typically comprise oxide or nitride, are then formed on the oxide liner adjacent to the sidewalls of the stacked gate structure and over the extension regions. After source and drain regions have been implanted, the conventional disposable spacers and oxide liner are removed by using an HF wet etch process. However, as a result of low selectivity between oxide and silicon, during removal of the conventional disposable spacers and oxide liner in the HF wet etch process, undesirable gouging can occur in the extension regions in the silicon substrate. Dopant loss that results from gouging in the extension regions can increase the resistance of the extension regions, which can cause a decrease in FET performance.
Thus, there is a need in the art for a disposable spacer process that provides disposable spacers that can be effectively removed during FET fabrication without causing gouging or dopant loss in the substrate.